mustang 77The hhest-performing GT Performance trim is the least efficient with ratings of 90 MPGe city and 77 MPGe hhway. We haven't yet had the 2025 MachRefinements in optional equipment and Decor groups focused on creature comfort, safety and fuel economy. Uncommon luxury in a sporty car introduced potential Ford Mustang buyers in the 1977 Ford Mustang's new brochure.